1. Field of the Invention
The present invention relates to mobile telecommunications systems, particularly though not exclusively the Universal Mobile Telecommunications System (UMTS).
2. Description of the Related Art
In systems such as UMTS and GSM, data is transmitted over the air interface as packets, and the length of the payload transported by a packet is indicated by the Length Indicator (LI) field contained in its header. In systems such as GSM, the LI values are defined in octets. In the UMTS system, the packets have a strictly defined structure and are known as Data Units, e.g. Protocol Data Units (PDU). Their format is defined in the 3GPP™ RLC Protocol Specification 3G TS 35.322, Section 9.2—Elements for Peer-to-Peer Communication—Formats and Parameters. Generally these Data Units have a header and one or more following payload units of data. Many of these Data Units have length indicator (LI) fields, e.g. UMD PDU and AMD PDU (unacknowledged/acknowledged mode data PDU). In UMTS, the length indicator (LI) gives the number of octets of the length of a data segment. The size of the length indicator may be either 7 or 15 bits. If more than one payload unit (PU) is transported in the packet additional length indicators can be used to indicate the limit between the different PU's. The length Indicator Field is also used to indicate the start of the padding area at the end of a packet.
With UMTS, some applications (e.g. Adaptive Multi Rate speech codecs) produce frames whose length is not a multiple value of 8 bits. Therefore, with such frames, there is no way to indicate to the peer-receiving end the exact length of the payload.